Q.Arrange the following structures in the order that a drop of water entering the nephron would encounter them.
a. Afferent arteriole
b. Bowman's capsule
c. Collecting duct
d. Distal tubule
e. Glomerulus
f. Loop of Henle
g. Proximal tubule
h. Renal pelvis

The kidney's microscopic working unit

Each human kidney contains close to a million nephrons, and every nephron has two parts: a filtering renal corpuscle and a long renal tubule.

Renal corpuscle

The renal corpuscle pairs a double-walled cup, Bowman's capsule, with a tuft of capillaries it encloses, the glomerulus. The capillary walls have pores (fenestrae); the inner (visceral) layer of Bowman's capsule is made of podocytes, cells with branching foot processes that wrap the capillaries and leave narrow filtration slits between them, while the outer (parietal) layer is simple squamous epithelium. Together the fenestrated endothelium, basement membrane and podocyte foot processes form a three-layered filter that holds back blood cells and large plasma proteins.

Renal tubule

From Bowman's capsule, the tubule runs on as the proximal convoluted tubule (PCT), then forms the U-shaped loop of Henle (thin descending limb, thick ascending limb), then coils again as the distal convoluted tubule (DCT), and finally opens into a straight collecting duct that carries urine through the medulla toward the calyces.

Cortical vs juxtamedullary nephrons

Nephrons whose loop of Henle barely dips into the medulla are cortical nephrons; those with long loops reaching deep into the medulla are juxtamedullary nephrons - it is this second group that makes concentrated urine possible.

Blood supply

Each nephron is served by two capillary beds in sequence: the glomerulus itself (fed by a wide afferent arteriole, drained by a narrower efferent arteriole - the size difference keeps glomerular pressure high), and the peritubular capillaries the efferent arteriole forms around the rest of the tubule. In juxtamedullary nephrons the efferent arteriole additionally forms the vasa recta, straight vessels running alongside the loop of Henle deep into the medulla.